Method for the drilling of oil wells

ABSTRACT

Method for the drilling of oil wells and for the positioning of the appropriate casings, consisting in drilling the well section of interest and, during the drilling, in maintaining a high degree of hole regularity by the use of automatic verticality and/or curvature control equipment. This method allows the positioning of casings with an almost constant clearance with values of +/−1.5 inches for the whole well depth (lean profile).

[0001] The present invention relates to an improved method for the drilling of oil wells which allows the positioning of lining columns, operating with an almost constant clearance for the whole of the desired well depth and which substantially consists in effecting the drilling, guaranteeing the elimination of any geometrical curvature and irregularities of the hole, whether it be vertical or deviated.

[0002] During the drilling of oil wells, lining operations of the hole (pipe-laying) are effected which comprise the positioning of appropriate casings at pre-established intervals in relation to the depth reached and characteristics of the formations penetrated.

[0003] During the pipe-laying, in order to guarantee easy descent of the lining columns into the well, it is generally necessary to ensure that the difference between the external casing diameter and the hole diameter (clearance) is maintained at sufficiently high values.

[0004] During conventional technological drilling, the clearance between casing and hole can vary from values of about 6-7 inches (15-16 cm) for the surface and/or intermediate phases, to values of almost an inch for the deeper phases (for example: 26″ hole for 20″ conductor pipe, 17½ hole for 13⅜″ , 12¼″ hole for 9⅝″ casing, 8½″ hole for 7″ casing).

[0005] The necessity of adopting high clearance values is linked to the high rigidity of pipes with a larger diameter/thickness and the impossibility of drilling perfectly vertical wells and/or with a controlled curvature. In fact, the poor flexibility of pipes together with a certain degree of hole irregularity (deviations, curving and/or narrowing) can make the lowering of columns into the well difficult especially during the surface and/or intermediate phases.

[0006] The necessity, according to the conventional technologies, of producing holes with a considerably larger diameter with respect to that of the casing to guarantee descent to the well bottom during the surface and intermediate phases, causes the formation of a large quantity of waste products and a long duration of the plant on the territory with consequent long times and high drilling costs.

[0007] The drilling method according to the present invention allows, with the same diameter of the production column, the dimensions of the upper well part (surface and intermediate columns) to be reduced. This enables a significant reduction in the consumption of materials (mud, cement and steel) and consequently the production of waste products. This technique also avoids the necessity of producing holes with a diameter which is too large with respect to the diameter of the columns to be lowered, which generally implies the possibility of effecting holes with a smaller diameter compared to the conventional technique. All of this positively influences the advancement rate of the bit therefore allowing the production times of the holes to be reduced, with a consequent decrease in the costs. The technique according to the present invention also enables a significant reduction in the operating costs, as the verticality and/or regular curvature of the well facilitates all workover and well intervention operations.

[0008] This method comprises a drilling and pipe-laying technique which allows the positioning of the lining columns operating with an almost constant clearance with values of more or less 1.5 inches (3-4 cm) for the whole well depth (from the top to the bottom), or in any case for the whole of the desired well depth. The fact that a reduced clearance is adopted, allows, with the same number of columns and final diameter of the production casing, the dimensions of the upper part of the well to be greatly reduced.

[0009] This solution is mainly suitable for applications in deep, vertical or deviated wells, also in the presence of formations with a low drilling capacity and/or difficulty in controlling the trajectory. In these cases the use of the technique according to the invention allows considerable time saving and reduction in the drilling costs.

[0010] An object of the present invention therefore relates to an improved method for the drilling of oil wells and for the contemporaneous positioning of appropriate casings, characterized in that the clearance is kept almost constant for the whole of the desired well depth, consisting in drilling the well section of interest, maintaining a high degree of hole regularity by the use of automatic verticality and/or curvature control equipment.

[0011] In particular, the method according to the following invention comprises effecting the drilling phase according to the following procedures:

[0012] automatic control of the verticality and/or curvature of the well;

[0013] use of bits equipped with adequate distributors and roller reamers, in order to guarantee hole regularity and calibration;

[0014] use of drilling mud with chemical and rheological characteristics which are such as to minimize any possible problems of hole instability;

[0015] constant control of all the drilling parameters in order to maintain a curvature (BUR/DO) of 0.7 degrees every 30 m, with a maximum slope of 1.5 degrees in the vertical sections.

[0016] For the automatic control of the well verticality, the use of the device called “Straight Hole Drilling Device (SDD)”, a drilling instrument produced by the Applicant in collaboration with Baker Hughes, has proved to be particularly advantageous. This device, contrary to the conventional systems, automatically effects a continuous correction of the verticality and is based on a retro-activated control which ensures the absolute verticality of holes, even in formations which have a strong tendency to cause the bit trajectory to deviate from the vertical.

[0017] The use of a device called Autotrak, a drilling instrument produced by the Applicant, again in collaboration with Baker Hughes, has proved to be advantageous for the automatic control of the curvature. This device effects a continuous correction of the curvature which guarantees an optimum geometry in the deviated sections.

[0018] A preview of both apparatuses produced in collaboration with Baker was provided in the paper SPE 50379 of November 1998.

[0019] Various alternatives are available on the market both for the automatic verticality control and curvature control, such as:

[0020] RDS of Camco;

[0021] AGS of Cambridge Automation

[0022] Well Director of Well Done

[0023] As an illustrative but non-limiting example of the method according to the present invention, the pipe-laying procedure is effected as follows.

[0024] After producing a perfectly vertical and well calibrated hole the lining columns can be lowered into the well. In order to facilitate the passage of the casing into the hole calibrated with a reduced clearance, the following precautions should be observed:

[0025] Use threaded connections of the flush or near-flush type. The integral connection called “ASFC” (Agip Semi Flush Connection) described in patent application 5934 filed on Feb. 19, 1999 by the same Applicant, can be advantageously used. This connection has a limited clearance (external diameter 2.5% higher than the external pipe diameter) and is characterized by a significant improvement in the compression and torque strength/efficiency, with respect to existing connections of the same category. The joint is also equipped with a double metal to metal seal which makes it suitable for applications in deep wells and/or in the presence of high pressures.

[0026] Check the perfect rectilinearity of the pipes. The tolerances admitted by the API regulation in terms of residual manufacturing deformations are not acceptable in effecting the Lean technique. The rectilinearity must therefore be accurately checked before beginning the piping operations.

[0027] Limit the use of centralizers (if necessary use an Integral Blade Centralizer).

[0028] During the pipe laying, limit the descent rate of the column to avoid forcing and the creation of dangerous ramming linked to the reduced ring dimensions.

[0029] Use cementation shoes of the centralized type (Stabilizer Shoe) equipped with an auto fill-up device.

[0030] During the cementation special malts with a high fluidity and mechanical resistance are used.

[0031] In the case of possible deviated sections, in addition to the following precautions, curvature should be planned in relation to the flexibility of the casings to be used.

[0032] Operating as described above, it was possible to lower a casing with an external diameter slightly less than that of the hole (about 1.5 inches ) into the well, creating a narrower pipe-laying profile (Lean), with the advantages described above and without jeopardizing the diameter of the production column.

[0033]FIG. 1 compares the conventional pipe-laying program with the “Lean” program. The data in said figure were obtained in the Monte Enoc 9 well effected in the Field of Val D'Agri in Basilicata. It is evident how with the “Lean” solution, starting from a lower diameter of the surface and intermediate columns, a production column is obtained with the same diameter as that produced with the conventional solution.

[0034]FIG. 2 describes a further two examples of Lean pipe-laying, which can provide a valid alternative to the previous scheme, above all in contingency situations.

[0035]FIG. 3 schematically represents a comparison between the hole sections. 

1. A method for the drilling of oil wells and positioning of the appropriate casings, consisting in drilling the well section of interest and, during the drilling, in maintaining a high degree of hole regularity by the use of automatic verticality and/or curvature control equipment.
 2. The method for the drilling of oil wells and positioning of the appropriate casings according to the previous claim, characterized in that the drilling phase is carried out observing the following precautions: automatic control of the verticality and/or curvature of the well using the device called “Straight Hole Drilling Device” (SDD); use of bits equipped with adequate distributors and roller reamers use of drilling mud with chemical and rheological characteristics which are such as to minimize any possible well instability problems constant control of all the drilling parameters in order to maintain a curvature (BUR/DO) of 0.7 degrees of every 30 m, with a maximum slope of 1.5 degrees in the vertical sections. 